Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a variety of signal transduction processes within the cell. Protein kinases, containing a similar 250-300 amino acid catalytic domain, catalyze the phosphorylation of target protein substrates. It is reported that many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events. These diseases include benign and malignant proliferation disorders, diseases resulting from inappropriate activation of the immune system, allograft rejection, graft vs host disease, autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
The kinases may be categorized into families by the substrates in the phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, lipids, etc.). Tyrosine phosphorylation is a central event in the regulation of a variety of biological processes such as cell proliferation, migration, differentiation and survival. Several families of receptor and non-receptor tyrosine kinases control these events by catalyzing the transfer of phosphate from ATP to a tyrosine residue of specific cell protein targets. Sequence motifs have been identified that generally correspond to each of these kinase families (Hanks et al., FASEB J., 1995, 9, 576-596; Knighton et al., Science, 1991, 253, 407-414; Garcia-Bustos et al., EMBO J., 1994, 13:2352-2361). Some non-limiting examples of the protein kinase include abl, Aurora, Akt, bcr-abl, BIk, Brk, Btk, c-kit, c-Met, c-src, c-fms, CDK1, CDK2, CDK3, CDK4, CDK5, CDK6, CDK7, CDK8, CDK9, CDK0, cRafl, CSF1 R, CSK, EGFR, ErbB2, ErbB3, ErbB4, Erk, Fak, fes, Flt-3, FGFR1, FGFR2, FGFR3, FGFR4, FGFR5, Fgr, Flt-1, Fps, Frk, Fyn, Hck, IGF-1 R, INS-R, JAK, KDR, Lck, Lyn, MEK, p38, PDGFR, P1K, PKC, PYK2, ros, Tie, Tie-2, TRK, Yes, and Zap70.
Aurora kinase family is a collection of highly related serine/threonine kinase that are key regulators of mitosis, essential for accurate and equal segtion of genomic material from parent to daught cells. Members of the Aurora kinase family include three related kinases known as Aurora-A, Aurora-B, and Aurora-C (also known as Aurora-1, Aurora-2, and Aurora-3). Despite significant sequence homology, the localization and functions of these kinases are largely distinct from one another (Richard D. Carvajal, et al. Clin Cancer Res., 2006, 12(23): 6869-6875; Daruka Mahadevan, et al., Expert Opin. Drug Discov., 2007 2(7): 1011-1026).
Aurora-A is ubiquitously expressed and regulates cell cycle events occurring from late S phase through M phase, including centrosome maturation (Berdnik D, et al., Curr Biol., 2002, 12: 640-647), mitotic entry (Hirota T, et al., Cell, 2003, 114:585-598; Dutertre S, et al., J Cell Sci., 2004, 117:2523-2531), centrosome separation (Marumoto T. et al. J Biol. Chem., 2003, 278:51786-51795), bipolar-spindle assembly (Kufer T A, et al. J Cell Biol., 2002; 158:617-623; Eyers P A, et al., Curr Biol., 2003; 13:691-697), chromosome alignment on the metaphase plate (Marumoto T, et al. J Biol Chem., 2003, 278:51786-51795; Kunitoku N, et al., Dev Cell., 2003, 5: 853-864), cytokinesis (Marumoto T, et al., J Biol. Chem., 2003, 278:51786-51795), and mitotic exit. Aurora-A protein levels and kinase activity both increase from late G2 through M phase, with peak activity in prometaphase. Once activated, Aurora-A mediates its multiple functions by interacting with various substrates including centrosomin, transforming acidic coiled-coil protein, cdc25b, Eg5, and centromere protein A.
Aurora-B is a chromosomal passenger protein critical for accurate chromosomal segregation, cytokinesis (Hauf S., et al. J Cell Biol., 2003, 161:281-94; Ditchfield C, et al., J Cell Biol., 2003, 161:267-80; Giet R, et al., J Cell Biol., 2001, 152:669-682; Goto H, et al., J Biol. Chem., 2003, 278:8526-8530), protein localization to the centromere and kinetochore, correct microtubule-kinetochore attachments (Murata-Hori M, et al., Curr. Biol., 2002, 12:894-899), and regulation of the mitotic checkpoint. Aurora-B localizes first to the chromosomes during prophase and then to the inner centromere region between sister chromatids during prometaphase and metaphase (Zeitlin S G, et al. J Cell. Biol., 2001, 155:1147-1157). Aurora-B participates in the establishment of chromosomal biorientation, a condition where sister kinetochores are linked to opposite poles of the bipolar spindle via amphitelic attachments. Errors in this process, manifesting as a merotelic attachment state (one kinetochore attached to microtubules from both poles) or a syntelic attachment state (both sister kinetochores attached to microtubules from the same pole), lead to chromosomal instability and aneuploidy if not corrected before the onset of anaphase. The primary role of Aurora-B at this point of mitosis is to repair incorrect microtubule-kinetochore attachments (Hauf S, et al., J Cell Biol., 2003, 161:281-294; Ditchfield C, et al., J Cell Biol., 2003, 161:267-280; Lan W, et al. Curr Biol., 2004, 14:273-286). Without Aurora-B activity, the mitotic checkpoint is compromised, resulting in increased numbers of aneuploid cells, genetic instability, and tumorigenesis (Weaver B A, et al., Cancer Cell., 2005, 8:7-12).
Aurora-A overexpression is a necessary feature of Aurora-A-induced tumorigenesis. In cells with Aurora-A overexpression, mitosis is characterized by the presence of multiple centrosomes and multipolar spindles (Meraldi P et al., EMBO J., 2002, 21:483-492). Despite the resulting aberrant microtubule-kinetochore attachments, cells abrogate the mitotic checkpoint and progress from metaphase to anaphase, resulting in numerous chromosomal separation defects. These cells fail to undergo cytokinesis, and, with additional cell cycles, polyploidy and progressive chromosomal instability develop (Anand S, et al., Cancer Cell, 2003, 3:51-62).
The evidence linking Aurora overexpression and malignancy proliferation disorders, such as colon, breast, lung, pancrease, prostate, bladder, head, neck, cervix, and ovarian cancers, liver, gastric and pancreatic tumors, has stimulated interest in developing Aurora inhibitors for cancer therapy. In normal cells, Aurora-A inhibition results in delayed, but not blocked, mitotic entry, centrosome separation defects resulting in unipolar mitotic spindles, and failure of cytokinesis (Marumoto T, et al., J Biol Chem., 2003, 278:51786-51795). Encouraging antitumor effects with Aurora-A inhibition were shown in three human pancreatic cancer cell lines (Panc-1, MIA PaCa-2, and SU.86.86), with growth suppression in cell culture and near-total abrogation of tumorigenicity in mouse xenografts (Hata T, et al., Cancer Res., 2005, 65:2899-2905).
Aurora-B inhibition results in abnormal kinetochore-microtubule attachments, failure to achieve chromosomal biorientation, and failure of cytokinesis (Goto H, et al. J Biol Chem. 2003, 278:8526-30; Severson AF1 et al. Curr Biol., 2000, 10:1162-1171). Recurrent cycles of aberrant mitosis without cytokinesis result in massive polyploidy and, ultimately, to apoptosis (Hauf S, et al., J Cell Biol., 2003, 161:281-294; Ditchfield C, et al., J Cell Biol., 2003, 161:267-80; Giet R, et al., J Cell Biol., 2001, 152:669-682; Murata-Hori M, Curr. Biol., 2002, 12:894-899; Kallio M J, et al., Curr Biol., 2002, 12:900-905).
Inhibition of Aurora-A or Aurora-B activity in tumor cells results in impaired chromosome alignment, abrogation of the mitotic checkpoint, polyploidy, and subsequent cell death. These in vitro effects are greater in transformed cells than in either non-transformed or non-dividing cells (Ditchfield C, et al. J Cell Biol., 2003, 161:267-280). Thus, targeting Aurora may achieve in vivo selectivity for cancer. Although toxicity to rapidly dividing cell of the hematopoietic and gastrointestinal system is expected, the activity and clinical tolerability shown in xenograft models indicates the presence of a reasonable therapeutic index. Given the preclinical antitumor activity and potential for tumor selectivity, several Aurora kinase inhibitors have been developed.
FLT3 (Flt3, FMS-related tyrosine kinase 3), also known as FLK-2 (fetal liver kinase 2) and STK-1 (human stem cell kinase 1), belongs to a member of the class III receptor tyrosine kinase (RTK-III) family that include KIT, PDGFR, FMS and FLT (Stirewalt D L, et al., Nat. Rev. Cancer, 2003, 3:650-665; Rosnet O, et al., Genomics 1991, 9:380-385; Yarden Y, et al., Nature, 1986, 323: 226-232; Stanley E R, et. al., J. Cell. Biochem, 1983, 21:151-159; Yarden Y, et al., EMBO J., 1987, 6:3341-3351). FLT3 is a membrane-spanning protein and composed of four domains; an extracellular ligand-binding domains consisting of five immunoglobin-like structures, a transmembrane (TM) domain, a juxtamembrane (JM) domain and a cytoplasmic C-Terminal tyrosine kinase (TK) domain. (Agnes F, et al., Gene, 1994, 145:283-288, Scheijen B, et al., Oncogene, 2002, 21:3314-3333).
The ligand for FLT3 (FLT3 or FL) was cloned in 1993 and shown to be a Type I transmembrane protein expressed in cells of the hematopoietic bone marrow microenvironment, including bone marrow fibroblasts and other cells (Lyman S D, et al. Cell 1993, 75:1157-1167). Both the membrane-bound and soluable forms can activate the tyrosine kinase activity of the receptor and stimulate growth of progenitor cells in the marrow and blood. Binding of ligand to receptor induces dimerisation of the receptor and activation of the kinase domains; which then autophosphorylate and catalyse phosphorylation of substrate proteins of various signal transduction pathways such as signal transducer and activator of transcription 5 (STAT5), RAS/mitogen-activated protein kinase (RAS/MAPK), phosphoinositide 3-kinase (PI3K), src homologous and collagen gene (SHC), SH2-containing inositol-5-phosphatase (SHIP), and cytoplasmic tyrosine phosphatase with 2 Src-homology 2 (SH2) domains (SHP2), which play important roles in cellular proliferation, differentiation, and survival (Dosil M, et al. Mol Cell Biol., 1993, 13:6572-6585. Zhang S, Biochem Biophys Res Commun., 1999, 254:440-445). In addition to hemotopoietic cells, FLT3 gene is also expressed in placenta, gonads and brain (Maroc N, et al. Oncogene, 1993, 8: 909-918) and also plays an important role in the immune response (deLapeyriere O, et al., Leukemia, 1995, 9:1212-1218).
FLT3 has also been implicated in hematopoietic disorders which are pre-malignant disorders including myeloproliferative disorders, such as thrombocythemia, essential thrombocytosis (ET), myelofibrosis (MF), chronic idiopathic myelofibrosis (IMF), and polycythemia vera (PV), pre-malignant myelodysplastic syndromes. Hematological malignancies include leukemias, lymphomas (non-Hodgkin's lymphoma), Hodgkin's disease (also called Hodgkin's lymphoma), and myeloma, for instance, acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), acute promyelocytic leukemia (APL), chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), chronic neutrophilic leukemia (CNL). FLT3 is overexpressed at the levels in 70-100% of cases of acute myeloid leukemias (AML), and in a high percentage of T-acute lymphocytic leukemia (ALL) cases (Griffin J D, et al., Haematol J. 2004, 5: 188-190). It is also overexpressed in a smaller subset of chronic myeloid leukemia (CML) in blast crisis. Studies have shown that the leukemic cells of B lineage ALL and AML frequently co-express FL, setting up autocrine or paracrine signaling loops that result in the constitutive activation of FLT3 (Zheng R, et. al., Blood., 2004, 103: 267-274). A high level of the FLT3 ligand is found in the serum of patients with Langerhans cell histocytosis and systemic lupus erythematosus, which further implicates FLT3 signaling in the dysregulation of dendritic cell progenitors in those autoimmune diseases (Rolland et al., J. Immunol., 2005, 174:3067-3071).
Evidence is rapidly accumulating that many types of leukemias and myeloproliferative syndromes have mutation in tyrosine kinases. FLT3 mutations are one of the most frequent somatic alterations in AML, occurring in approximately ⅓ of patients. There are two types of activating mutations in FLT3 described in patients with leukemia. These include a spectrum of internal tandem duplications (ITD) occurring within the auto-inhibitory juxtamembrane domain (Nakao M, et al., Leukemia, 1996, 10:1911-1918; Thiede C, et al., Blood, 2002, 99:4326-4335), and activation loop mutations that include Asp835Tyr (D835Y), Asp835Val (D835V), Asp835His (D835H), Asp835Glu (D835E), Asp835Ala (D835A), Asp835Asn (D835N), Asp835 deletion and Ile836 deletion (Yamamoto Y1 et al., Blood 2001: 97:2434-2439; Abu-Duhier F M, et al., Br. J. Haematol., 2001, 113:983-988). Internal tandem duplication (ITD) mutations within the JM domain contribute to about 17-34% of FLT3 activating mutations in AML. FLT3-ITD has also been detected at low frequency in myelodysplastic syndrome (MDS) (Yokota S, et al., Leukemia, 1997, 11:1605-1609; Horiike S, et al., Leukemia, 1997, 11:1442-1446). The ITDs are always in-frame, and are limited to the JM domain. However, they vary in length and position from patient to patient. These repeat sequences may serve to disrupt the autoinhibitory activity of the JM domain resulting in the constitutive activation of FLT3. Both FLT3-ITD and FLT3-Asp835 mutations are associated with FLT3 autophosphorylation and phosphorylation of downstream targets (Mizuki M, et al. Blood, 2000, 96:3907-3914; Mizuki M, et al. Blood, 2003, 101:3164-3173; Hayakawa F, et al., Oncogene, 2000, 19: 624-631).
Inhibitors of FLT3 are presently being studied and have reached clinical trials as monotherapy in relapsed or refractory AML patients, some or all of whom had FLT3 mutations. Collectively, these data suggest that FLT3 is an attractive therapeutic target for the development of kinase inhibitors for AML and other associated diseases.
Janus kinase (JAK) is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. The JAK family plays a role in the cytokine-dependent regulation of proliferation and function of cells involved in immune response. Cytokines bind to their receptors, causing receptor dimerization, and this enables JAKs to phosphorylate each other as well as specific tyrosine motifs within the cytokine receptors. STATs that recognize these phosphotyrosine motifs are recruited to the receptor, and are then themselves activated by a JAK-dependent tyrosine phosphorylation event. Upon activation, STATs dissociate from the receptors, dimerize, and translocate to the nucleus to bind to specific DNA sites and alter transcription.
Currently, there are four known mammalian JAK family members: JAK1 (Janus kinase-1), JAK2 (Janus kinase-2), JAK3 (Janus kinase, leukocyte; JAKL; L-JAK and Janus kinase-3) and TYK2 (protein-tyrosine kinase 2). While JAK1, JAK2 and TYK2 are ubiquitously expressed, JAK3 is reported to be preferentially expressed in natural killer (NK) cells and not resting T cells (“Biology and significance of the JAK/STAT signaling pathways.” Growth Factors, April 2012; 30(2): 88).
JAK1 is essential for signaling for certain type I and type II cytokines. It interacts with the common gamma chain (γc) of type I cytokine receptors to elicit signals from the IL-2 receptor family, the IL-4 receptor family, the gp130 receptor family. It is also important for transducing a signal by type I (IFN-α/β) and type II (IFN-γ) interferons, and members of the IL-10 family via type II cytokine receptors. Genetic and biochemical studies have shown that JAK1 is functionally and physically associated with the type I interferon (e g., IFNalpha), type II interferon (e.g., IFNgamma), IL-2 and IL-6 cytokine receptor complexes. Furthermore, characterization of tissues derived from JAK1 knockout mice demonstrated critical roles for this kinase in the IFN, IL-IO, IL-2/IL-4, and IL-6 pathways.
Expression of JAK1 in cancer cells enables individual cells to contract, potentially allowing them to escape their tumor and metastasize to other parts of the body. Elevated levels of cytokines which signal through JAK1 have been implicated in a number of immune and inflammatory diseases. JAK1 or JAK family kinase inhibitors may be useful for modulating or treating in such diseases. (Kisseleva et al., 2002, Gene 285:1-24; Levy et al., 2005, Nat. Rev. Mol. Cell Biol. 3:651-662). A humanized monoclonal antibody targeting the IL-6 pathway (Tocilizumab) was approved by the European Commission for the treatment of moderate-to-severe rheumatoid arthritis (Scheinecker et al., 2009, Nat. Rev. Drug Discov. 8:273-274).
JAK2 is implicated in signaling by members of the type II cytokine receptor family (e.g. interferon receptors), the GM-CSF receptor family, the gp130 receptor family. JAK2 signaling is activated downstream from the prolactin receptor. Studies have identified a high prevalence of an acquired activating JAK2 mutation (JAK2V617F) in myleoproliferative disorders such as polycythemia vera, essential thrombocythemia and idiopathic myelofibrosis, etc. The mutant JAK2 protein is able to activate downstream signaling in the absence of cytokine stimulation, resulting in autonomous growth and/or hypersensitivity to cytokines and is believed to play a role in driving these diseases. Additional mutations or translocations resulting dysregulated JAK2 function have been described in other malignancies (Ihle J. N. and Gilliland D. G., Curr. Opin. Genet. Dev., 2007, 17:8; Sayyah J. and Sayeski P. P., Curr. Oncol. Rep., 2009, 11: 117). Inhibitors of JAK2 have been described to be useful in myeloproliferative diseases (Santos et al, Blood, 2010, 115:1131; Barosi G. and Rosti V., Curr. Opin. Hematol, 2009, 16:129, Atallah E. and Versotvsek S., Exp. Rev. Anticancer Ther. 2009, 9:663).
JAK3 associates exclusively with the gamma common cytokine receptor chain, which is present in the IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 cytokine receptor complexes. JAK3 is predominantly expressed in immune cells and transduces a signal in response to its activation via tyrosine phosphorylation by interleukin receptors. Since JAK3 expression is restricted mostly to hematopoietic cells, its role in cytokine signaling is thought to be more restricted than other JAKs. Mutations of JAK3 result in severe combined immunodeficiency (SCID). (O'Shea et al., 2002, Cell, 109 (suppl.): S121-S131). Based on its role in regulating lymphocytes, JAK3 and JAK3-mediated pathways have been targeted for immunosuppressive indications (e.g., transplantation rejection and rheumatoid arthritis) (Baslund et al., 2005, Arthritis & Rheumatism 52:2686-2692; Changelian et al., 2003, Science 302: 875-878).
TYK2 is implicated in IFN-α, IL-6, IL-10 and IL-12 signaling. Biochemical studies and gene-targeted mice uncovered the crucial role of TYK2 in immunity. Tyk2-deficient mice are viable and fertile but display multiple immunological defects, most prominently high sensitivity to infections and defective tumor surveillance. In contrast, inhibition of TYK2 results in increased resistance against allergic, autoimmune and inflammatory diseases. Particularly, targeting Tyk2 appears to be a promising strategy for the treatment of IL-12-, IL-23- or Type 1 IFN-mediated diseases. These include but are not limited to rheumatoid arthritis, multiple sclerosis, lupus, psoriasis, psoriatic arthritis, inflammatory bowel disease, uveitis, sarcoidosis, and tumors (Shaw, M. et al, Proc. Natl. Acad. Sci. USA, 2003, 100, 11594-11599; Ortmann, R. A., and Shevach, E. M. Clin. Immunol, 2001, 98, 109-118; Watford et al, Immunol. Rev., 2004, 202: 139). [“Janus Kinase (JAK) Inhibitors in Rheumatoid Arthritis.” Current Rheumatology Reviews, 2011, 7, 306-312].
A fully human monoclonal antibody targeting the shared p40 subunit of the IL-12 and 11-23 cytokines (Ustekinumab) was recently approved by the European Commission for the treatment of moderate-to-severe plaque psoriasis (Krueger et al., 2007, N. Engl. J. Med. 356:580-92; Reich et al., 2009, Nat. Rev. Drug Discov. 8:355-356). In addition, an antibody targeting the IL-12 and IL-23 pathways underwent clinical trials for treating Crohn's Disease (Mannon et al., 2004, N. Engl. J. Med. 351: 2069-79).
When dysregulated, JAK-mediated responses can positively or negatively affect cells leading to over-activation and malignancy or immune and hematopoietic deficiencies, respectively, and suggests the utility for use of inhibitors of JAK kinases. The JAK/STAT signaling pathway is involved in a variety of hyperproliferative and cancer-related processes including cell-cycle progression, apoptosis, angiogenesis, invasion, metastasis and evasion of the immune system (Haura et al., Nature Clinical Practice Oncology, 2005, 2(6), 315-324; Verna et al., Cancer and Metastasis Reviews, 2003, 22, 423-434). In addition, the JAK/STAT signaling pathway is important in the genesis and differentiation of hematopoietic cells and regulating both pro- and anti-inflammatory and immune responses (O'Sullivan et al., Molecular Immunology 2007, 44:2497).
Therefore, the JAK/STAT pathway, and in particular all four members of the JAK family, are believed to play a role in the pathogenesis of the asthmatic response, chronic obstructive pulmonary disease, bronchitis, and other related inflammatory diseases of the lower respiratory tract. The JAK/STAT pathway has also been implicated to play a role in inflammatory diseases/conditions of the eye including, but not limited to, iritis, uveitis, scleritis, conjunctivitis, as well as chronic allergic responses. Since cytokines utilize different patterns of JAK kinases (O'Sullivan et al., Mol. Immunol, 2007, 44:2497; Murray J., Immunol, 2007, 178:2623), there may be utility for antagonists of JAK kinases with differing intra-family selectivity profiles in diseases associated with particular cytokines or in diseases associated with mutations or polymorphisms in the JAK/STAT pathways.
Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic joint inflammation. Patients with rheumatoid arthritis treated with JAK inhibitor showed that inhibition of JAK1 and JAK3 blocks signalling by multiple cytokines that are important for lymphocyte function, including interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15 and IL-21. [Fleischmann, R. et al. “Placebo-controlled trial of tofacitinib monotherapy in rheumatoid arthritis.” N. Engl. J. Med. 367, 495-507 (2012)]. It was conjectured that small-molecule inhibitors that directly inactivate specific JAK isoforms would also reduce not only the clinical symptoms of RA, but also suppress the upregulation of many of the proinflammatory cytokines that are critical in driving RA disease progression. [“Inhibitors of JAK for the treatment of rheumatoid arthritis: rationale and clinical data.” Clin. Invest. (2012) 2(1), 39-47]
Persistent activation of STAT3 or STATS has been demonstrated in a wide spectrum of solid human tumors including breast, pancreatic, prostate, ovarian and hepatic carcinomas, as well as in the majority of hematopoietic tumors including lymphomas and leukemias. In this context, inactivation of JAK/STAT signaling in many hematopoietic tumors resulted in inhibition of cell proliferation and/or induction of apoptosis. Although STAT3 in tumor cells can be activated by various kinases, JAK2 has been shown to be the most important upstream activator mediating STAT3 activation in human tumor cell lines derived from various solid tumors [Mohamad Bassam Sonbol, Belal Firwana, Ahmad Zarzour, Mohammad Morad, Vishal Rana and Ramon V. Tiu “Comprehensive review of JAK inhibitors in myeloproliferative neoplasms.” Therapeutic Advances in Hematology 2013, 4(1), 15-35; Hedvat M, Huszar D, Herrmann A, Gozgit J M, Schroeder A, Sheehy A, et al. “The JAK2 inhibitor AZD1480 potently blocks Stat3 signaling and oncogenesis in solid tumors.” Cancer Cell 2009; 16(6):487-97.]. Therefore, inhibition of JAK kinases may have a beneficial role in the therapeutic treatment of these diseases.
Clearly, protein kinase inhibitors have gathered attention as a new drug category for both immunosuppression and antiinflammatory drug, and for cancer drug. Thus, new or improved agents which inhibit protein kinases such as Aurora inhibitors, FLT3 inhibitors and Janus kinases inhibitors are continually needed that act as immunosuppressive agents for organ transplants, and antitumor agents, as well as agents for the prevention and treatment of autoimmune diseases (e.g., multiple sclerosis, psoriasis, rheumatoid arthritis, asthma, type I diabetes, inflammatory bowel disease, Crohn's disease, polycythemia vera, essential thrombocythemia, myelofibrosis, autoimmune thyroid disorders, Alzheimer's disease), diseases involving a hyperactive inflammatory response (e.g., eczema), allergies, chronic obstructive pulmonary disease, bronchitis, cancer (e.g., prostate, acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphocytic leukemia, leukemia, multiple myeloma), and some immune reactions (e.g., skin rash or contact dermatitis or diarrhea) caused by other therapeutics, to name a few. The compounds, compositions and methods described herein are directed toward these needs and other ends.